1. Field of the Invention
This invention relates in general to data storage systems, and more particularly to a method and apparatus for calibrating a tape transport servo system.
2. Description of Related Art
Data loss is a serious threat to companies of all sizes, and catastrophic data loss can destroy a business. But most data loss isn""t the result of a big disaster, it""s caused by human error, viruses, and disk malfunctions. A suitable backup routine provides the best protection against data loss of all kinds. And tape technology remains the most efficient and cost-effective means to perform system backup, whether for a small business or a global 24xc3x977 operation.
Tape remains unrivaled in terms of cost and capacity for data storage, and should play an increasing crucial role in corporate data protection strategies. No other technology offers the same combined low cost and high capacity advantage of tape. While other technologies may offer strengths in one or more areas, overall, they do not meet the entire set of customer needs that tape addresses.
Tape drives make backup fast, easy, reliable and affordable. Speed is critical because your data is constantly growing while the time available for backup is shrinking. Even the slowest tape drive writes 1 MB per second and the fastest 30 MB per second, which means a 200 GB backup can be completed in less than two hours. Furthermore, unlike other storage methods, tape drives offer a range of media that allows you to back up all the data on a small to medium-sized server. Tape backup also captures system setup information, as well as data, allowing an entire system to be restored in the event a disaster strikes. Also, backups can be scheduled to occur automatically at a time determined to be most convenient.
Another area where tape storage excels is when it comes to data protection. Tape has proved itself a reliable medium, and tape drives themselves have never been more reliable. Easily portable, tapes have the added advantage of being simple to remove and store offsite, so keeping a disaster recovery copy is less of a burden. In terms of affordability, tape is the most cost-effective way to store large amounts of data per gigabyte of storage. The compact size of tape cartridges also helps keep down your storage costs.
Modern tape transport servo systems which move tape directly from one tape reel to the other in order to transport tape over the recording head must control tape tension, position and velocity to the requirements of the head to tape interface. The servo control parameters at the recording head, namely tension, velocity and position, must be directly controlled by the reel drive motors. In low cost tape drives, the high resolution tachometers associated with reel motor control are eliminated, and the control problem is made more difficult. In addition, as tape thickness is reduced to increase tape length and cartridge data capacity, it is necessary to reduce the nominal tension level in the tape transport to avoid overstressing the thin tape.
The electrical and mechanical component tolerances in the two motor control channels of a tape transport system typically are +/xe2x88x9215% of the nominal component values. In addition, there are some parameters, such as motor friction, which are not well specified, and which can vary by large amounts, typically factors of 2 or 3 to 1. The motor friction is a critical mechanical parameter in the control of tape tension, and directly changes the tension at the head if it varies from the assumed value in the control system.
It can be seen then that there is a need for a method and apparatus to calibrate the motor analog channel circuits, the motor power drivers, and the motor electromechanical parameters, in order to reduce the manufacturing tolerances, purchase tolerances and time varying parameters that directly affect tension, velocity and position control.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for calibrating a tape transport servo system.
The present invention solves the above-described problems by exciting the two reel motors of the tape transport at a time when tape is not being controlled by the servo system and gathering calibration data during this time.
A method in accordance with the principles of the present invention includes a exciting tape reel motors when the tape drive is not being controlled by the tape transport servo system and collecting calibration data for the motor torque, motor friction, DAC offsets, and pulse width modulator control signal timing.
Other embodiments of a method in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the collecting of calibration data for the pulse width modulator (PWM) control signal timing further includes enabling the drive amplifiers to activate the pulse width modulator control signals, measuring the on-time and the off-time for the pulse width modulator control signal, averaging the on-time and off-time measurements to reduce measurement noise and storing the averaged measured values for each reel motor driver.
Another aspect of the present invention is that the collecting of calibration data for the motor friction and DAC offsets further includes setting reel motors at a constant speed in a forward direction, when constant speed in the forward direction has been established, accumulating a value of each of the motor drive DACs at predetermined time intervals for a preset time period, at the end of the preset time period, storing the motor friction values into motor friction registers, wherein the value stored in the motor friction register represent the number of predetermined time intervals collected times the forward friction current for the motors, copying accumulated DAC values into DAC offset calibration registers, setting reel motors at constant speed in the backward direction, when constant speed in the backward direction has been established, accumulating a value of each of the motor drive DACs at the predetermined time intervals for the preset period of time, subtracting DAC values collected in the backward direction from the DAC values copied into the DAC offset registers after the forward collection and dividing the values of the motor friction registers and the DAC offset registers by the sum of the number of predetermined time intervals spanning the forward and backward collection to yield the final values for calibration of motor friction and DAC offset.
Another aspect of the present invention is that the collecting of calibration data for the motor torque further includes setting motor drive DACs to zero when the motors are rotating in the forward direction so that motor current is set at zero and the motors are coasting in a forward direction, measuring the motor torque constants for the forward direction by integrating the motor generated voltage over a fixed angle of motor rotation for each motor, storing the integrated motor torque constant from the forward measurement in a motor voltage integration register for each motor, setting motor drive DACs to zero when the motors are rotating in the backward direction so that motor current is set at zero and the motors are coasting in a backward direction, measuring the motor torque constants for the backward direction by integrating the motor generated voltage over a fixed angle of motor rotation for each motor and storing the integrated motor torque constant from the backward measurement in a motor voltage integration register for each motor to arrive at an integral of motor voltage over two revolutions.
Another aspect of the present invention is that the collecting of calibration data for the motor friction and DAC offsets further includes setting reel motors at a constant speed in a forward direction, when constant speed in the forward direction has been established, accumulating a value of each of the motor drive DACs at predetermined time intervals for a preset time period, at the end of the preset time period, storing the motor friction values into motor friction registers, wherein the value stored in the motor friction register represent the number of predetermined time intervals collected times the forward friction current for the motors, copying accumulated DAC values into DAC offset calibration registers, setting reel motors at constant speed in the backward direction, when constant speed in the backward direction has been established, accumulating a value of each of the motor drive DACs at the predetermined time intervals for the preset period of time, subtracting DAC values collected in the backward direction from the DAC values copied into the DAC offset registers after the forward collection and dividing the values of the motor friction registers and the DAC offset registers by the sum of the number of predetermined time intervals spanning the forward and backward collection to yield the final values for calibration of motor friction and DAC offset.
Another aspect of the present invention is that the collecting of calibration data for the motor torque further includes setting motor drive DACs to zero when the motors are rotating in the forward direction so that motor current is set at zero and the motors are coasting in a forward direction, measuring the motor torque constants for the forward direction by integrating the motor generated voltage over a fixed angle of motor rotation for each motor, storing the integrated motor torque constant from the forward measurement in a motor voltage integration register for each motor, setting motor drive DACs to zero when the motors are rotating in the backward direction so that motor current is set at zero and the motors are coasting in a backward direction, measuring the motor torque constants for the backward direction by integrating the motor generated voltage over a fixed angle of motor rotation for each motor and storing the integrated motor torque constant from the backward measurement in a motor voltage integration register for each motor to arrive at an integral of motor voltage over two revolutions.
In another embodiment of the present invention a method for calibrating pulse width modulator control signal timing is disclosed. The method includes exciting tape reel motors when the tape drive is not being controlled by the tape transport servo system and collecting calibration data for the pulse width modulator control signal timing by enabling the drive amplifiers to activate the pulse width modulator control signals, measuring the on-time and the off-time for the pulse width modulator control signal, averaging the on-time and off-time measurements to reduce measurement noise and storing the averaged measured values for each reel motor driver.
In another embodiment of the present invention a method for calibrating motor friction and DAC offsets is disclosed. The method includes exciting tape reel motors when the tape drive is not being controlled by the tape transport servo system and collecting calibration data for motor friction and DAC offsets by setting reel motors at a constant speed in a forward direction, accumulating a value of each of the motor drive DACs at predetermined time intervals for a preset time period when constant speed in the forward direction has been established, storing the motor friction values into motor friction registers at the end of the preset time period, wherein the value stored in the motor friction register represent the number of predetermined time intervals collected times the forward friction current for the motors, copying accumulated DAC values into DAC offset calibration registers, setting reel motors at constant speed in the backward direction, accumulating a value of each of the motor drive DACs at the predetermined time intervals for the preset period of time when constant speed in the backward direction has been established, subtracting DAC values collected in the backward direction from the DAC values copied into the DAC offset registers after the forward collection and dividing the values of the motor friction registers and the DAC offset registers by the sum of the number of predetermined time intervals spanning the forward and backward collection to yield the final values for calibration of motor friction and DAC offset.
In another embodiment of the present invention a method for calibrating the motor torque is disclosed. The method includes exciting tape reel motors when the tape drive is not being controlled by the tape transport servo system and collecting calibration data for the motor torque by setting motor drive DACs to zero when the motors are rotating in the forward direction so that motor current is set at zero and the motors are coasting in a forward direction, measuring the motor torque constants for the forward direction by integrating the motor generated voltage over a fixed angle of motor rotation for each motor, storing the integrated motor torque constant from the forward measurement in a motor voltage integration register for each motor, setting motor drive DACs to zero when the motors are rotating in the backward direction so that motor current is set at zero and the motors are coasting in a backward direction, measuring the motor torque constants for the backward direction by integrating the motor generated voltage over a fixed angle of motor rotation for each motor and storing the integrated motor torque constant from the backward measurement in a motor voltage integration register for each motor to arrive at an integral of motor voltage over two revolutions.
In another embodiment of the present invention a method for calibrating a tape transport servo system for a tape drive is disclosed. The method includes clearing motor calibration data, performing pulse width modulator control signal timing measurements to obtain offset timings for each of the reel motors, accelerating the reel motors up to speed in the forward direction to collect DAC offset data, motor friction data and motor torque data, accelerating the reel motors up to speed in the backward direction to collect DAC offset data, motor friction data and motor torque data, processing the gathered calibration parameters for the pulse width modulator control signal timing, DAC offsets, the motor friction and the motor torque to arrive at final calibration data for use in the tape transport servo control system and storing the final calibration data into a calibration data structure.
Another aspect of the present invention is that the processing further comprises scaling the motor torque constant for use in the tape transport servo control system, wherein the scale factor for torque constant from summation of e(t) over two revolutions is given by SF=(total angle)*(volt-scale-factor)*(1/torque-Q-factor)*(sample-frequency).
In another embodiment of the present invention a tape drive is disclosed. The tape drive includes a controller configured to calibrate a tape transport servo system by exciting tape reel motors when the tape drive is not being controlled by the tape transport servo system and collecting calibration data for the motor torque, motor friction, DAC offsets, and pulse width modulator control signal timing.
In another embodiment of the present invention a tape drive is disclosed. The tape drive includes a controller configured to calibrate a tape transport servo system by clearing motor calibration data, performing pulse width modulator control signal timing measurements to obtain offset timings for each of the reel motors, accelerating the reel motors up to speed in the forward direction to collect DAC offset data, motor friction data and motor torque data, accelerating the reel motors up to speed in the backward direction to collect DAC offset data, motor friction data and motor torque data, processing the gathered calibration parameters for the pulse width modulator control signal timing, DAC offsets, the motor friction and the motor torque to arrive at final calibration data for use in the tape transport servo control system and storing the final calibration data into a calibration data structure.
In another embodiment of the present invention an article of manufacture comprising a program storage medium readable by a computer is disclosed. The medium tangibly embodies one or more programs of instructions executable by the computer to perform a method for calibrating a tape transport servo system, wherein the method includes exciting tape reel motors when the tape drive is not being controlled by the tape transport servo system and collecting calibration data for the motor torque, motor friction, DAC offsets, and pulse width modulator control signal timing.
In another embodiment of the present invention an article of manufacture comprising a program storage medium readable by a computer is disclosed. The medium tangibly embodies one or more programs of instructions executable by the computer to perform a method for calibrating a tape transport servo system, wherein the method includes clearing motor calibration data, performing pulse width modulator control signal timing measurements to obtain offset timings for each of the reel motors, accelerating the reel motors up to speed in the forward direction to collect DAC offset data, motor friction data and motor torque data, accelerating the reel motors up to speed in the backward direction to collect DAC offset data, motor friction data and motor torque data, processing the gathered calibration parameters for the pulse width modulator control signal timing, DAC offsets, the motor friction and the motor torque to arrive at final calibration data for use in the tape transport servo control system and storing the final calibration data into a calibration data structure.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.